Number bases

problem
Knapsack

Age

14 to 16

Challenge level

You have worked out a secret code with a friend. Every letter in the alphabet can be represented by a binary value.
problem
Secret transmissions

Age

14 to 16

Challenge level

How can Agent X transmit data on a faulty line and be sure that her message will get through?
problem
Guesswork

Age

14 to 16

Challenge level

Ask a friend to choose a number between 1 and 63. By identifying which of the six cards contains the number they are thinking of it is easy to tell them what the number is.
problem
More secret transmissions

Age

16 to 18

Challenge level

In 'Secret Transmissions', Agent X could send four-digit codes error free. Can you devise an error-correcting system for codes with more than four digits?